Question about B&K AVR-202
THIS 1972 SILVERFACE BASSMAN 100 HUMMING AMP ...WHEN YOU OPEN THE BACK THE SMALL TUBE ON FAR LEFT IS NOT BURNING BRIGHTLY LIKE THE OTHERS....IT APPEARS TO HAVE ALL THE 6L6 POWER TUBES REPLACED WITH RECENT SOVTEKS...
Well where do I begin. First, the polarity switch on the back might eliminate or reduce the hum, but by todays standards the way it functions is a deadly safety hazard (remember all the musicians that got fried in the '60's and early '70's?). That circuitry should be disabled and the unit retrofitted with a 3 prong power cord.
Next, the tube filiments are powered by AC voltage, and there is a control on the chassis for balancing it in order to reduce the hum. It could be toast or mis-adjusted. There could be a tube or other component problem causing your hum. The DC power supply could have faulty filter capacitors.
Another source of problems in these amps are the carbon resistors that introduce static noise in the audio. These should be changed to much better carbon film resistors.
If you are not comfortable working on electronic equipment with voltages in excess of 300VDC you should bring it to a pro audio repair shop.
Posted on Apr 28, 2009
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Posted on Jan 02, 2017
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